Infrared sensor

ABSTRACT

A low noise, high sensitivity and wide dynamic range uncooled type infrared sensor can effectively reduce the influence of fluctuations of the gate of the amplifier transistor. The infrared sensor comprises an imaging region containing thermoelectric conversion pixels arranged two-dimensionally in the form of a matrix of a plurality of row and a plurality of columns on a semiconductor substrate to detect incident infrared rays, column selection lines, vertical signal lines, said column selection lines and said vertical signal lines being arranged the imaging region, amplifier transistors configured to be modulated by the respective signal voltages generated in the signal lines, storage capacities connected respectively to the drains of the amplifier transistors and configured to store signal charges from the transistors, a plurality of reset circuits for resetting the drain potentials of said amplifier transistors and read circuits for reading the respective signal charges stored in said storage capacities, coupling capacitors being arranged between the vertical signal lines and the gate of amplifier transistors, sampling transistors being connected between the drains and the gates of said amplifier transistors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefits of priority fromthe prior Japanese Patent Applications No. 2000-91173 filed on Mar. 27,2001 and No. 2001-95301 filed on Mar. 29, 2001, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to an infrared sensor and, more particularly, itrelates to a signal read circuit of a thermal type infrared sensor.

The technology of infrared imaging can find a broad scope of applicationbecause images can be picked up regardless of day or night even throughsmoke and fog to provide a great advantage over visible light imaging.Additionally, infrared imaging can obtain thermal information on theobject of imaging. The broad scope of application of infrared imagingcovers military defense devices, monitor cameras and fire detectioncameras.

In recent years, massive efforts have been paid for developing nocooling thermal type infrared solid state imaging devices that do notrequire the use of a cooling mechanism for low temperature operationsbecause the need of using a cooling mechanism is the largest problem ofquantum type infrared solid state imaging devices that have been in themain stream. Thermal type infrared solid state imaging devices are sodesigned that the incoming infrared rays with a wavelength of about 10ìm are transformed into heat by means of an IR rays absorption systemand the temperature change of the heat sensing section produced by theweak heat is converted into an electric signal by means of athermoelectric converter. Then, infrared image information can beobtained by reading the electric signal.

Thermal type infrared solid state imaging devices realized by formingsilicon pn junctions for converting a temperature change into a voltagechange by means of a constant forward electric current in an SOI(silicon on insulator) region have been reported (Tomohiro Ishikawa, etal., Proc. SPIE Vol. 3698, p 556, 1999).

Silicon pn junction type devices using an SOI substrate provide anadvantage that they can be manufactured by using only a silicon LSImanufacturing process and hence are highly adapted to mass production.

Another advantage of silicon pn junction type devices is that the pnjunctions that operate as thermoelectric conversion means have a pixelselecting function of utilizing the current rectifying ability of pnjunctions and therefore it is possible to simplify the internalstructure of pixels.

Meanwhile, the temperature change in the pixel section of a thermal typeinfrared solid state imaging device is generally about 5×10⁻³ times ofthe temperature change of the object of imaging although it may varydepending on the absorption coefficient of the infrared rays absorptionlayer and the performance of the optical system. In other words, whenthe temperature of the object of imaging changes by 1[K], the pixeltemperature changes by 5[mK].

When eight silicon pn junctions are connected in series to a singlepixel, the thermoelectric conversion efficiency is in the order of about10 [mV/K]. Therefore, when the temperature of the object of imagingchanges by 1[K], a signal voltage of 50 [ìV] is generated in the pixelsection.

In reality, the thermal type infrared solid state imaging device isrequired to detect a temperature change of about 0.1 [K]. Then, it hasto read a generated voltage signal of about 5 [ìV].

As means for reading such a very weak signal voltage, a circuit adaptedto amplify the generated signal voltage as the gate voltage of a MOSamplifier transistor for amplifying the electric current and integratethe amplified current with time by means of a storage capacitor isknown.

Such a circuit is referred to as gate modulation integration circuit. Aneffect of limiting the signal bandwidth and reducing the random noisecan be achieved by arranging such a circuit as column amplifying circuitin each column of a matrix for the purpose of parallel amplification ofthe electric current of a row.

The voltage gain: G of a gate modulation integration circuit isdetermined by the mutual conductance of the amplifiertransistor:gm=äId/äVg, the integration time:ti and the storage capacityCi and expressed by G=(ti×gm)/Ci. When the integration time:ti and thestorage capacity:Ci are given, the gain is dominated by the mutualconductance:gm of the amplifier transistor. The value of gm isapproximately expressed by formula (1) below when an n-type MOStransistor operates in a saturation region;

gm=(W/L)·(åox/Tox)·ìn·(Vgs−Vth)  (1),

where W: channel width,

L: channel length,

åox: dielectric constant of gate oxide film,

Tox: film thickness of gate oxide film,

ìn: electron mobility,

Vgs: gate/source voltage and

Vth: threshold voltage of transistor.

As pointed out above, a thermal type infrared solid state imaging deviceis required to detect a temperature change of about 0.1[K] in thetemperature of the object of imaging. Therefore, it is necessary to reada signal of about 5 [ìV] that is generated in the pixel section. Thisvoltage level is very low if compared with a CMOS sensor that is used toobtain an image by means of visible light. According to Nakamura andMatsunaga, “High Sensitivity Image Sensor”, the Journal of the Instituteof Image Information and Television Engineers, Vol. 54, No. 2, p. 216,2000, the noise voltage is about 0.4 [mV]=400 [ìV]. In view of thisnoise level, the noise level of the above infrared solid state imagingdevice is as low as about {fraction (1/80)} of that of a CMOS sensor andhence the signal voltage the former deals is as low as about {fraction(1/80)} of that of the latter.

Therefore, if the sensor output is processed by means of a circuitsimilar to a circuit to be for processing the output of a CMOS sensorthat is a typical imaging device, a column amplifier comprising gatemodulation integration circuits and showing a gain of about 80 timeswill be required.

However, a variance greater than the pixel output of about 5 [ìV] isfound at the gate of the amplifier transistor of a gate modulationintegration circuit and hence such a circuit needs to be designed with arelatively low gain. The variance is attributable to the variance of thethreshold voltage of the MOS amplifier transistors and that of thethreshold of the load MOS transistors to be used as constant currentsource and it is known that both show an amplitude of about 30 [mV].

The amplitude of the fluctuations of the threshold voltage means thatthe storage capacity can show fluctuations of about 2.4[V] when an about80 times greater gain is used as design value because the fluctuationsare amplified by the amplifier/read circuit like the pixel output signalapplied as the gate voltage of the amplifier transistor. Of course, thefluctuations of the thresholds are specific to the individual MOSamplifier transistors and the individual load MOS transistors and afixed pattern appears in the picked up image so that the obtained imagecan be corrected by means of an external circuit. However, suchcorrections use most of the voltage swing of the storage capacitor andexpand the dynamic range that the external circuit is required to show.

Therefore, until now, the load applied to the external circuit has to beinevitably reduced at the cost of the gain of the amplifier/readcircuit. Furthermore, it has not been possible to sufficiently suppressrandom noises such as current shot noises and 1/f noises of theamplifier/read circuit in order to secure a large gain.

Additionally, in many cases, an electric current has to be made to flowto the thermoelectric converter of the thermal type infrared sensor inorder to read the thermal information of the thermoelectric converter aselectric signal. Then, a so-called self heating problem arises becauseJoule's heat is generated due to the bias current or the bias voltage tobe used for reading the thermal information and the generated Jole'sheat by turn heats the thermoelectric converter.

For instance, when thermoelectric conversion pixels are mounted onto asemiconductor substrate and the general value of 10⁻⁷ [W/K] is selectedfor the thermal conductance between the semiconductor substrate and thepn junction type thermoelectric converter, the influence of self heatingof the converter will be a temperature rise of about 30[K] if computedon an assumption that the number of pn junctions is eight, the biascurrent is 200 [ìA], the pixel selection period for signal reading is 25[ìs] and the frame rate is 60 [fps]. The importance of solving theproblem of self heating will be realized if the above value is comparedwith the pixel temperature rise of 5 [mK] due to the received infraredrays described earlier.

FIG. 26 of the accompanying drawings schematically illustrates thetemperature change (in terms of voltage Vsig) of a pixel due to selfheating. As shown, the pixel temperature rises rapidly as the pixel isselected in a row selection period and falls gradually after the pixelselection pulse becomes off due to the thermal time constant of thethermoelectric converter.

Thus, the temperature change due to self heating is 30[k] according tothe above computation while the temperature signal generated by theincoming infrared rays that give rise to a temperature change of onlyabout 5 [mK] is smaller than the height of the solid line in FIG. 26.Thus, in the case of an ordinary column amplifier connected to a signalline, a weak electric current flows in the initial stages of pixelselection and the signal current increases with time due to self heatingduring the pixel selecting operation. Additionally, the electric currentis almost totally occupied by the temperature information currentproduced by the self heating, which is a mere noise current.

FIG. 27 of the accompanying drawings schematically illustrates theintegrated and stored electric charge in a storage capacitor that isdepicted as a potential well and located at the output side of thecolumn amplifier. As seen from FIG. 27, the stored electric charge ismostly the electric charge QSH that is attributable to self heating andthe signal charge Qsig is only a minor part thereof.

FIG. 27 also shows that the electric current generated in a latter halfof the row selection period becomes relatively large as a result of thetemperature change caused by self heating and consequently theinformation obtained in the latter half and in the final stages of therow selection period is weighted. Then, as a matter of course, theeffective sampling period is curtailed to expand the signal bandwidthand increase random noise.

X. Gu, et al. reports a method for avoiding the problem of self heatingby forming a bridge circuit, using a bolometer operating on theprinciple of temperature change of electric resistance (X. Gu, et al.,Sensors and Actuators A, Vol. 69, p. 92, 1998).

The authors of the above document formed a bridge circuit to realizedifferential amplification by arranging an insensitive reference pixelhaving a heat capacitance same as that of the ordinary pixels andshowing a low thermal resistance at each column.

This is a method utilizing the fact that the temperature rise due toself heating in the row selection period that is very short relative tothe thermal time constant is mainly governed by the heat capacitance.

However, while this method is effective for reducing the influence ofself heating, it is an approximate solution to the problem of selfheating and does not completely dissolve the self heating problem.

Insensitive reference pixels have to be provided on a one to one basisrelative to the sensitive pixels for the purpose of completelydissolving the self heating problem in a rigorous sense of the words.However, no image sensor having a layout of arranging pixelstwo-dimensionally has ever been realized to date.

This is because, when an insensitive reference pixel is provided foreach ordinary pixel in order to form a bridge circuit, there arises adisadvantage that the sensitivity of the image sensor is reduced to lessthan a half if the pixel size of the reference pixel is same as that ofan ordinary pixel. Therefore the effect of dissolving the problem ofself heating is offset by this disadvantage and hence such a techniqueof canceling self heating by means of a bridge circuit may not beeffective.

In view of the above identified circumstances, it is therefore an objectof the present invention to provide a low noise, high sensitivity andwide dynamic range uncooled type infrared sensor that can effectivelyreduce the influence of fluctuations of the gate of the amplifiertransistor and a method of driving such an infrared sensor.

The self heating problem of pn junction type infrared sensors comprisingthermoelectric conversion pixels having a column amplifier has not beendissolved in the technological field of the present invention.Therefore, another object of the present invention is to solve thisproblem.

BRIEF SUMMARY OF THE INVENTION

In an aspect of the present invention, there is provided an infraredsensor comprising:

an imaging region containing thermoelectric conversion pixels arrangedtwo-dimensionally in the form of a matrix of a plurality of row and aplurality of columns on a semiconductor substrate to detect incidentinfrared rays;

a plurality of row selection lines arranged in the column direction inthe imaging region;

a plurality of signal lines arranged in the row direction in saidimaging region;

a plurality of amplifier transistors having respective gates connectedto said signal lines and configured to be modulated by the respectivesignal voltages generated in the signal lines;

a plurality of storage capacities connected respectively to the drainsof the amplifier transistors and configured to store signal charges fromthe transistors;

a plurality of reset circuits connected to the respective drains of saidamplifiers to reset the drain potentials of said amplifier transistorsand make them show a predetermined potential;

a plurality of read circuits for reading the respective signal chargesstored in said storage capacities;

a plurality of coupling capacities arranged respectively between saidsignal lines and the gates of said amplifier transistors; and

a plurality of sampling transistors connected respectively between thedrains and the gates of said amplifier transistors to selectivelyturning them on to apply the threshold information of said transistorsto the gates.

Some of modes of carrying out the invention includes the following.

(1) Each of the thermoelectric conversion pixels comprises an infraredabsorbing section for absorbing infrared rays striking the semiconductorsubstrate and converting them into heat; a thermoelectric conversionsection for converting the temperature change produced by the heatgenerated in the infrared absorbing section into an electric signal, apixel selection circuit for selecting a pixel to be used for reading thepixel output signal from the thermoelectric conversion section and anoutput circuit for outputting the pixel output signal from the selectedthermoelectric conversion pixel.

(2) The semiconductor substrate is an SOI substrate SOI formed by layingan SOI single crystal silicon layer on a single crystal siliconsupporting substrate by way of a silicon oxide layer and thethermoelectric conversion means comprises single crystal silicon pnjunctions formed by arranging second conductivity type regions in theinside of the first conductivity type SOI single crystal silicon layerand supported on the cavities of the cavity structure formed in theinside of the SOI substrate.

(3) The imaging region contains at least a row of insensitive pixelsshowing no sensitivity relative to incident infrared rays and hencebeing not apt to change any pixel output signal by incident infraredrays, said insensitive pixels being arranged in the row direction.

(4) The insensitive pixels are made insensitive as the thermoelectricconversion means is not thermally separated from the semiconductorsubstrate.

(5) The infrared sensor further comprises a storage means for storing afirst group of pieces of row output information obtained from the readmeans on a time series basis and a correction means for correcting asecond group of pieces of row optical information obtained by selectinga row different from the row used for obtaining the first group ofpieces of row output information.

An infrared sensor having the above configuration is typically driven ina manner as described below. During a non-selection period when any ofsaid thermoelectric conversion pixels is selected by means of said rowselection lines in a single frame period, the drain potentials of theamplifier transistors are held in an unreset state by turning off saidreset means and the drains and the gates of the transistors areconnected and made to show a same potential by turning on said samplingtransistors in the first period of the non-selection period. In a secondperiod of said non-selection period not including the first period, thedrains and the gates of the sampling transistors are separated form eachother by turning off said sampling transistors and the gates of saidamplifier transistors are made to hold the drain potentials of therespective transistors obtained in the first period. During a selectionperiod for selecting a thermoelectric conversion pixel by means of saidrow selection lines and a period for reading the signal voltages by saidread means, the sampling transistors are held to an off state.

An infrared sensor comprising an insensitive pixel row is typicallydriven in a manner as described below.

During a first selection period when the insensitive pixel row isselected by means of said row selection lines, the drain potentials ofthe drains of said amplifier transistors are held to an unreset state byturning off said reset means and the drains and the gates of saidsampling transistors are connected and made to show a same electricpotential by turning on said sampling transistor to apply a first sourcevoltage to the sources of said amplifier transistors in a first periodof said first selection period. In a second period of said selectionperiod not including the first period, the drains and the gates of thesampling transistors are separated form each other by turning off saidsampling transistors and the gates of said amplifier transistors aremade to hold the drain potentials of the respective transistors obtainedin the first period. During a second selection period for selecting asensitive pixel row by means of said row selection lines in a singleframe period, said sampling transistors are held to an off state and asecond source voltage different from the first source voltage is appliedto the sources of said amplifier transistors. In a period for readingthe signal voltage of the selected amplifier transistor by means of saidrow selection lines by said read means, said sampling transistors areheld to an off state and the first source voltage is applied to thesources of said sampling transistor.

Thus, according to the present invention, the signal lines where thepixel output appears and the gates of the amplifier transistors areseparated from each other DC-wise by arranging coupling capacitorsbetween them and each frame is made to hold the threshold information ofthe amplifier transistors of each column in the gates of the amplifiertransistors in order to eliminate any variance among the voltage gainsof the columns that can be produced as a result of fluctuations of thethreshold value of the amplifier transistors, which may vary from columnto column. Thus, the influence of fluctuations of the threshold value ofeach column can be eliminated to make it no longer necessary to providea margin for the operating voltage region of the storage capacitors forthe purpose of coping with such fluctuations and securing a voltageswing of the storage capacitors. Therefore, according to the invention,it is possible to design a large gain for the gate modulationintegration circuit so that a highly sensitive uncooled type infraredsensor can be realized. Additionally, the potential of the storagecapacitor can be fully exploited for the same reason to make it possibleto provide a uncooled type infrared sensor having a wide dynamic range.

Thus, according to the invention, fluctuations of the threshold voltageof the amplifier transistors and the variance of operation point arecorrected at the same time by sampling the threshold information of theamplifier transistors of each column and also the threshold informationof the load MOS transistors of each column simultaneously at a timingwhen an insensitive pixel voltage is generated in the signal lines atthe time of selecting an insensitive pixel that contains thresholdinformation of the load MOS transistors. Thus, the influence offluctuations of the threshold voltage of the load MOS transistors ofeach column can be eliminated to make it no longer necessary to providea margin for the operating voltage region of the storage capacitors forthe purpose of coping with such fluctuations and securing a voltageswing of the storage capacitors. Therefore, according to the invention,it is possible to design a large gain for the gate modulationintegration circuit so that a highly sensitive uncooled type infraredsensor can be realized. Additionally, the potential of the storagecapacitor can be fully exploited for the same reason to make it possibleto provide an uncooled type infrared sensor having a wide dynamic range.

Instill another aspect of the invention, there is provided an infraredsensor comprising:

a plurality of thermoelectric conversion pixels arranged in the form ofa matrix of a plurality of rows and a plurality of columns andconfigured to thermoelectrically transform the heat generated as aresult of absorbing incident infrared rays and take it out as a changein the resistance;

a plurality of selection lines connected respectively to either the rowsor the columns of said thermoelectric conversion pixels;

a plurality of signal lines connected respectively to either the columnsor the rows, whichever appropriate, of said thermoelectric conversionpixels;

a pixel selection circuit for selectively applying a read voltage tosaid thermoelectric conversion pixels connected to said the selectionlines on a selection line by selection line basis and causing saidsignal lines to generate a voltage output signal;

an output signal amplifying circuit having a first input section and asecond input section, said first input section being connected to saidsignal lines, and configured to amplify the voltage output signal fromsaid thermoelectric conversion pixels; and

a compensation voltage applying circuit connected to the second inputsection of said output signal amplifying means and applying a waveformvoltage for canceling or reducing the voltage component contained insaid voltage signal due to the resistance change component attributableto the self heating produced in said thermoelectric conversion pixels bysaid read current in synchronism with said read voltage.

With an infrared sensor in this aspect of the invention, a ramp or stepwaveform voltage that is synchronized with the pixel selection pulse isapplied to the sources of the amplifying MOS transistors of theamplifying circuit to whose gates the voltage signal is input from thethermoelectric conversion section in order dissolve the self heatingproblem of the thermoelectric conversion section of a thermal typeinfrared sensor according to the invention that is attributable to theJoule's heat generated as a result of pixel selection. As a result, thevoltage attributable to self heating can be removed from the gate/sourcevoltage:Vgs of the amplifier transistors to realize a low noise, highsensitivity and wide dynamic range uncooled type infrared sensor.

Additionally, according to the invention, it is possible to provide aninsensitive pixel column formed by arranging a heat isolationinsensitive pixel on each row. It is then possible to remove the voltageattributable to self heating from the gate/source voltage:Vgs of theamplifier transistors by applying a voltage produced by referring to theoutput voltage of the insensitive pixel column to the sources of saidamplifier transistors as in the case of applying a ramp waveformvoltage. Thus, it is also possible to realize a low noise, highsensitivity and wide dynamic range uncooled type infrared sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram of the first embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration.

FIG. 2A is a schematic plan view of the first embodiment, showingthermoelectric conversion pixels.

FIG. 2B is a cross sectional view of the first embodiment taken alongline A—A in FIG. 2A.

FIG. 3 is a timing chart illustrating the method of driving the firstembodiment of infrared sensor.

FIG. 4 is a timing chart illustrating the method of driving the secondembodiment of infrared sensor.

FIG. 5 is a schematic circuit diagram of the third embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration.

FIG. 6A is a schematic plan view of the third embodiment, showingthermoelectric conversion pixels.

FIG. 6B is a cross sectional view of the third embodiment taken alongline A—A in FIG. 6A.

FIG. 7 is a schematic circuit diagram of am embodiment obtained bymodifying the third embodiment.

FIG. 8 is a timing chart illustrating the method of driving the fourthembodiment of infrared sensor.

FIG. 9 is a timing chart illustrating the method of driving the fifthembodiment of infrared sensor.

FIG. 10 is a schematic circuit diagram of the sixth embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration.

FIG. 11 is timing chart illustrating the method of driving the sixthembodiment of infrared sensor.

FIG. 12 is a schematic circuit diagram of the seventh embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration.

FIG. 13 is a timing chart illustrating the method of driving the seventhembodiment of infrared sensor.

FIG. 14 is also a timing chart illustrating the method of driving theseventh embodiment of infrared sensor.

FIG. 15 is a schematic circuit diagram of the eighth embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration.

FIG. 16 is a timing chart illustrating a method of driving the eighthembodiment of infrared sensor.

FIG. 17 is also a timing chart illustrating another method of drivingthe eighth embodiment of infrared sensor.

FIG. 18 is a schematic circuit diagram of the ninth and tenthembodiments of infrared sensor according to the invention, illustratingits entire configuration.

FIG. 19 is a waveform graph, illustrating the ninth embodiment.

FIG. 20 is a waveform graph, illustrating the tenth embodiment.

FIG. 21 is a schematic circuit diagram of the eleventh embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration.

FIG. 22 is a waveform graph, illustrating the eleventh embodiment.

FIG. 23 is a schematic circuit diagram of the twelfth embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration.

FIG. 24 is a waveform graph, illustrating the twelfth embodiment.

FIG. 25 is a schematic circuit diagram of the thirteenth embodiment ofinfrared sensor according to the invention, illustrating itsconfiguration.

FIG. 26 is a graph illustrating how the pixel temperature Td and theoutput signal voltage Vsig abruptly change due to self heating during acolumn selection period and how the pixel temperature is restored in aframe period.

FIG. 27 is a schematic illustration of a potential well, showing howsignal charge Qsig and noise charge QSH attributable to selfhyper-heating are stored in a storage capacitor in the columnamplification circuit during a pixel selection period.

DETAILED DESCRIPTION OF THE INVENTION

(1st Embodiment)

FIG. 1 is a schematic circuit diagram of the first embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration. While pixels are arranged in two rows and two columns inFIG. 1 for the purpose of simplification, it may be needless to say thatthe embodiment can comprise more pixels arranged in the form of a matrixof m rows and n columns.

Thermoelectric conversion pixels 1 for converting incoming infrared raysinto an electric signal are arranged two-dimensionally on asemiconductor substrate to form an imaging region 3. A plurality of rowselection lines 4 (4-1, 4-2) and a plurality of vertical signal lines 5(5-1, 5-2) are arranged in the inside or the imaging region 3.

A row selection circuit 40 and a horizontal (column) selection circuit70 to be used for the purpose of pixel selection are arrangedrespectively in the row direction and in the column direction in theimaging region 3. The row selection lines 4 are connected to the rowselection circuit 40 while horizontal selection transistors 61, 62 areconnected to the horizontal selection circuit 70 by way of respectivehorizontal selection lines(7-1, 7-2). Load MoS transistors 8 (8-1, 8-2)are connected respectively to the vertical signal lines of the differentcolumns as constant current sources in order to obtain a pixel outputvoltage. Substrate voltage Vs is applied to the sources of the load MOStransistors 8.

Supply voltageVd is applied to the row selection line 4 selected by therow selection circuit 40 while the substrate voltage Vs is applied tothe unselected row selection line 4. As a result, the pn junctionlocated in the inside of the thermoelectric conversion pixel 1 of theselected row is forwardly biased and a bias current flows to it so thatthe operation point is determined by the temperature of the pn junctionin the pixel and the forward bias current to generate a pixel signaloutput voltage in the vertical signal line 5 of each column. At thistime, the pn junction of the pixel 1 not selected by the row selectioncircuit 40 is reversely biased. Thus, the pn junction in the inside ofeach pixel has a pixel selecting function.

The voltage generated in the vertical signal lines 5 is a very lowvoltage. Assume that the ratio of the temperature change of the objectof imaging is dTs to the temperature change of the pixel dTd is 5×10⁻³.Then, it will be appreciated that the voltage generated in the verticalsignal lines 5 is as low as 5 [ìV] form this value and thethermoelectric conversion sensitivity dV/dTd=10 [mV/K] that is obtainedwhen the eight pn junctions of the pixels are connected in series.Therefore, in order to recognize this temperature difference on theobject of imaging, the noise that is generated in the vertical signallines 5 needs to be made lower than 5 [ìV]. This noise level is as lowas about {fraction (1/80)} of the noise of a CMOS sensor that is usedfor a MOS type visible light image sensor.

An amplifying/read circuit 9 is provided for each column and the gate 10g of the amplifier transistor 10 of each column and the vertical signalline 5 of the column are capacitively coupled to each other by acoupling capacitor 11 in order to amplify this low signal voltage. Thevertical signal line 5 and the amplifying/read circuit 9 are isolatedDC-wise from each other by the coupling capacitor 11.

A storage capacitor 12 is connected to the drain 10 d side of theamplifier transistor 10 for integrating and storing the amplified signalcurrent. The storage time for integrating the signal current isdetermined by the row select pulse applied to the row selection lines 4by the row selection circuit 40. A reset transistor 13 for resetting thevoltage of the storage capacitor 12 is connected to the storagecapacitor 12 so that the storage capacitor 12 is reset by the voltageapplied to the gate RS after the completion of the operation by thehorizontal selection transistor 61 of reading the signal voltage.

The drain 10 d of the amplifier transistor 10 is connected to the gateof the amplifier transistor 10 by way of sampling transistor 15 so thatthe gate 10 g and the drain 10 d of the amplifier transistor 10 shows asame potential when the sampling transistor 15 is turned on.

FIGS. 2A and 2B schematically illustrate the structure of the infraredsensing thermoelectric conversion pixel 1 of this embodiment shown inFIG. 1. FIG. 2A is a schematic plan view of the first embodiment,showing thermoelectric conversion pixels and FIG. 2B is a crosssectional view of the first embodiment taken along line A—A in FIG. 2A.The thermoelectric conversion pixel 1 contains pn junction regions 115for thermoelectric conversion. More specifically, the thermoelectricconversion pixel 1 comprises infrared absorbing sections 118, 120, pnjunction regions 115 located in the inside of SOI layers 108 and formedfor thermoelectric conversion, a wire 117 connecting them and athermoelectric conversion section 110 arranged in buried silicon oxidefilm layer 114 supporting the SOI layers 108, all of which are arrangedon a cavity structure 107 formed in the inside of a single crystalsilicon semiconductor substrate 2. For the convenience of explanation,FIGS. 2A and 2B show a diode structure of arranging two pn junctionregions. The thermoelectric conversion pixel 1 further comprises asupport section 111 supporting the pixel 1 by way of the cavity bottomsection 107, or a cavity structure, and cavity lateral sections 119 andadapted to output an electric signal from the pixel 1 and a connectionsection (not shown) connecting the column signal line 5, or the verticalsignal line, and the row selection line 4. The heat emission of thepixel proceeds slowly so that the temperature modulation of the element1 by the incident infrared rays is conducted efficiently due to the factthat the pixel 1 and the support section 111 are arranged on a cavitystructure 107.

FIG. 3 is a timing chart illustrating the method of driving the firstembodiment of infrared sensor, which is applicable when the embodimentcomprises four pixels arranged in the form of a matrix of two rows andtwo columns as shown in FIG. 1. The source potential of the load MOStransistor 8 and the source potential of the amplifier transistor 10that are not shown in the timing chart are equal to the substratevoltage Vs, while the drain voltage of the reset transistor 13 that isnot shown in the timing chart either is made equal to the supply voltageVd.

Referring to FIG. 3, a non-selection period 100 during which the rowselection circuit 40 does not select any row precedes period 101 duringwhich the first row selection line 4-1 is selected as shown on the firstline of FIG. 3. An operation of obtaining and storing the thresholdinformation of the amplifier transistor 10 is performed in thisnon-selection period 100. The voltage of the vertical signal lines 5 ismade equal to the source voltage of the load MOS transistor 8 and henceto the substrate potential in this non-selection period 100.

Firstly, the reset transistor 13 is turned on to reset the voltages Vc1,Vc2 of the storage capacitor 12. Then, the sampling transistor (SMP) 15is turned on and the drain voltage of the amplifier transistor 10 thatis reset to the supply voltage Vd is applied to the gate 10 g of theamplifier transistor 10 during the non-selection period 100. Thus, theamplifier transistor 10 is turned on and a drain current flows. Thedrain voltage Vc falls as a result of the drain current to consequentlyreduce the conductance of the amplifier transistor 10 so that the drainvoltage Vc is made equal to the gate voltage and hence the drain currentno longer flows. This voltage is the threshold voltage of the amplifiertransistor 10 of each row.

The threshold information is held in the coupling capacitor 11 as thesampling transistor 15 is turned off after the threshold information ofthe amplifier transistor 10 is read to the gate voltage as sampledvalue. The threshold information is read once within a frame periodbefore the selection of the first row but not before the selection ofthe second row and the following rows. Thus, the threshold informationheld before the selection of the first row is used thereafter.

During the row selection period 101 shown on the first line in FIG. 3, arow selection pulse V1 is applied to the first row selection line 4-1and the bias current whose value is determined by the load transistor 8flows the current path formed by the load transistor 8, the verticalsignal line 5, the first row pixel 1, the first row selection line 4-1and the row selection circuit 40. The operation point of the pixel 1 isdetermined by the bias current and the temperature of the pn junctionsthat are the thermoelectric conversion means of the pixel 1 and a pixeloutput voltage that changes as a function of the temperature of thepixel 1 is generated in the vertical signal line 5 of each column. Then,the voltage of the vertical signal line 5 changes from the substratevoltage to the pixel output voltage.

The voltage change of the vertical signal line 5 by turn changes thegate voltage of the amplifier transistor 10 due to the coupling causedby the coupling capacitor 11. Thus, the gate voltage of the amplifiertransistor 10 becomes to be equal to the threshold information of theamplifier transistor 10 held in the non-selection period 100 plus thepixel output voltage information. As a result, the amplifier transistor10 is turned on and the drain current that corresponds to the verticalsignal line voltage flows. The electric current is integrated in thestorage capacitor 12 during the first row selection period 101 to changethe drain voltage Vc. At this time, the gate voltage that governs thedrain current of the amplifier transistor 10 is not affected by thethreshold value that can vary from column to column because it isdetermined by the extent of the shift from the held threshold voltage.

During the horizontal read period 102 that follows the selection period101, the horizontal read transistors 61, 62 are sequentially selected bythe horizontal selection circuit 70 and the drain voltages Vc1, Vc2 areread to the output line 24 on a time series basis. The operation of thesecond row and that of any of the following rows are similar to that ofthe first row except the sampling transistor 15 does not operate. Thus,the drain currents during the respective row selection periods areintegrated and sequentially read out.

As described above, with this embodiment, the threshold information ofthe amplifier transistor 10 that varies from column to column is held tothe coupling capacitor 11 that is connected to the gate of the amplifiertransistor 10 because of the threshold read operation during thenon-selection period 100. Therefore, the operation of integrating theelectric current during the row selection period 101 is not affected bythe variance of the threshold value of the amplifier transistor 10 andhence the drain current is determined only by the pixel output voltageproduced on the vertical signal line 5.

Thus, for the operation of the amplifying/read circuit 9 that istriggered by the integration of the drain current, it is no longernecessary to provide a margin for the purpose of preventing saturationof the storage capacitor 12 that can be caused by the fluctuations ofthreshold value of about 30 mV that is by far higher than the pixelsignal voltage produced on the vertical signal line 5 with a magnitudeof ìV. As a result, it is now possible to obtain a high voltage gain tosignificantly reduce the influence of noise to the amplifying/readcircuit 9 and the downstream circuits. Thus, according to the invention,there is provided an uncooled type infrared sensor with a low noise,high sensitivity and wide dynamic range.

The operation of the amplifying/read circuit 9 of this embodiment can beoptimized in terms of gain and saturation by means of the source voltageof the load MOS transistor 8, the selection pulse voltage of the rowselection circuit 40, the source voltage of the amplifier transistor 10and the drain voltage of the reset transistor 13.

(2nd Embodiment)

FIG. 4 is a timing chart illustrating the method of driving the secondembodiment of infrared sensor.

This embodiment of infrared sensor has a configuration same as the firstembodiment illustrated in FIGS. 1 and 2. It will be appreciated that thetiming chart of FIG. 4 of this embodiment is substantially same as thetiming chart of FIG. 3 of the first embodiment. However, the timingchart (FIG. 4) of this embodiment differs from that of the firstembodiment in that the source voltage SS of the amplifier transistor 10is driven by a pulse. In other words, a pulse voltage is applied to thesource SS of the amplifier transistor 10 for the threshold informationacquiring operation of the amplifier transistor 10 during thenon-selection period 100.

With this drive arrangement, the operation point of the flow path of thebias current including the pixel 1 in the row selection period is notchanged to make it possible to regulate the voltage between the gate andthe source of the amplifier transistor 10 during the amplifying/readoperation so that the operation point of the amplifying/read circuit 9can be regulated with ease to make it operate in an optimal condition.Thus, according to the invention, there is provided an uncooled typeinfrared sensor with a low noise, high sensitivity and wide dynamicrange.

(3rd Embodiment)

FIG. 5 is a schematic circuit diagram of the third embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration. In FIG. 5, the circuit configuration of the sensor isillustrated in a simplified form if compared with FIG. 1. It will beappreciated that 25 pixels are arranged in the form of a matrix of 5rows and 5 columns. In FIG. 5, the components same as or similar tothose of the FIG. 1 are denoted respectively by the same referencesymbols and will not be described any further.

A row selection pulse is applied to the row selection line 4 selected bythe row selection circuit 40 and the bias current supplied from aconstant current circuit 80 comprising load MOS transistors is made toflow to the pixel 1 of the selected row by way of the correspondingvertical signal line 5 to produce a pixel output voltage, whichcorresponds to the operation points of the pn junctions of the pixelthat are determined as a function of the bias current and thetemperature of the pixel 1, on the vertical signal line 5. The verticalsignal line 5 is connected to column amplifying/read circuit 90 by wayof a threshold holding circuit 140 comprising coupling capacitors 11 andsampling transistors 15. The grouped pieces of signal voltageinformation Vout for a row amplified in the column amplifying/readcircuit 90 are sequentially read out from horizontal read circuit 60 tooutput terminal 24 by the horizontal selection circuit 70.

An insensitive pixel row 200 formed by insensitive pixels 201 showing nosensitivity to infrared rays is arranged in the imaging region of thisembodiment and the row selection circuit 40 can select an insensitivepixel 201 by means of a row selection means as in the case of selectingan ordinary pixel 1.

As shown in FIGS. 6A and 6B, each thermally isolated insensitive pixel201 has a structure substantially same as that of an ordinary pixelshown in FIG. 2 except only that the former is provided on the infraredabsorbing section 118 with an infrared reflecting layer 130 made ofmetal film such as aluminum film.

Thus, incident infrared rays are reflected by the infrared reflectinglayer 130 of the thermally isolated insensitive pixel 201 so that notemperature change occurs in the pixel if infrared rays come in and thepixel outputs only a self heating signal to the vertical signal line 5when it is selected. Since no temperature change occurs if infrared rayscome in, the pixel operates as insensitive pixel that is not sensitiveat all to infrared rays.

As the sensor comprising an insensitive pixel row 200 in the imagingregion as shown in FIG. 5 is driven by means of the timing chart of FIG.3, the insensitive pixel row 200 provides output information. The noiselevel of the sensor can be reduced further by acquiring the output ofthe insensitive pixel row 200. More specifically, reset noise occurs inthe coupling capacitor 11 when the threshold information of theamplifier transistor 10 is held to the coupling capacitor 11. The resetnoise is same throughout the columns in a frame period because thethreshold information is held for a frame period. Therefore, it ispossible to eliminate the noise by reading the signal of the insensitivepixel row 200 and processing the signal by means of an external circuitto see the difference between the output of the insensitive pixel row200 and that of the ordinary pixel row. Thus, according to theinvention, it is possible to provide an uncooled type infrared sensorwith a low noise, high sensitivity by using an insensitive pixel row200.

If the coupling capacitance is Cc, the Boltzmann constant is k and theabsolute temperature of the device is T, the reset noise is expressed by(kT/Cc)^(1/2). If Cc=1pF, the reset noise will be as large as 60 ìv.This value is less than {fraction (1/100)} of the variance (about 30 mV)of the threshold value of the amplifier transistor 10 and hence it isnot necessary to provide a margin for the operation of theamplifying/read circuit 9. Additionally, while a vertical strip-likefixed pattern noise may be generated in a frame, such a noise can beeliminated by determining the difference between the output of anordinary pixel and an insensitive pixel, utilizing the correlationthereof in the frame. Therefore, the reset noise does not constitute anyincrease to the overall noise.

Additionally, as shown in FIG. 7, it is also possible to provide withinthe chip a memory circuit 311 for holding the pieces of outputinformation of a row and a correction circuit 312 for correcting theoutput from a row different from the row for which the pieces of outputinformation are held by means of those pieces of output information.

(4th Embodiment)

FIG. 8 is a timing chart illustrating the method of driving the fourthembodiment of infrared sensor. It is adapted to drive an infrared sensorcomprising pixels arranged in the form of a matrix of two rows and twocolumns. FIG. 8, the timing chart of the top line is used to drive aninsensitive pixel row.

This embodiment of infrared sensor has a configuration same as that ofthe third embodiment illustrated in FIG. 5. While a matrix of two rowsand two columns is used in FIG. 8 for the purpose of simplicity, it willbe appreciated that an infrared sensor comprising pixels arranged infive rows and five columns can be driven in a similar way.

In this embodiment, the threshold information of the amplifiertransistor 10 is read not in a non-selection period but in a selectionperiod 103 of the insensitive pixel row. Since the threshold informationis read in a period 103 for selecting the insensitive pixel row 200, apulse voltage is applied to the source SS of the amplifier transistorduring the selection period 103. The threshold information read duringthe selection period 103 of the insensitive pixel row is then read tothe output line 24 as a result of that the horizontal read transistors14 are sequentially selected by the horizontal selection circuit 6 inthe immediately following horizontal read period 104.

Thus, in this embodiment, the offset voltage added to the thresholdinformation that is read to the coupling capacitor 11 can be regulatedby means of the pulse voltage applied to the source of the amplifiertransistor. Therefore, it is possible to regulate the operation point ofthe amplifying/read circuit 9. As a result of carrying out the operationof reading the threshold information during the selection period 103 ofthe insensitive pixel row 200, not only the threshold information of theamplifier transistor 10 but also the threshold information of the loadMOS transistor 8 that operates as constant current source are read.Then, even a greater gain may be selected for the amplifying/readcircuit 9 so that it is possible to provide a low noise, highsensitivity and wide dynamic range uncooled type infrared sensor.

(5th Embodiment)

FIG. 9 is a timing chart illustrating the method of driving the fifthembodiment of infrared sensor. The timing chart is adapted to drive apixel arrangement of two rows and three column, of which the first rowis an insensitive pixel row.

In this embodiment, the row selection circuit 40 selects twice theinsensitive pixel row 200. The threshold information is read in thefirst row selection period 103 and the insensitive pixel output isobtained in the second row selection period 105. The thresholdinformation obtained in the first row period 103 is hold in the couplingcapacitor 11 by SMP pulse operation. The insensitive pixel output readin the selection period 105 is read out in the immediately followinghorizontal read period 106.

Thus, with the timings of FIG. 9, both the operation of reading thethreshold value by an insensitive pixel and that of reading theinsensitive pixel output can be performed with the structure having asingle row of insensitive pixels. Then, the influence of variance of thethreshold value of the amplifier transistor 10 can be eliminated byreading the threshold value and the reset noise of the couplingcapacitor 11 can be eliminated by reading the insensitive pixel outputand determining the difference between the insensitive pixel output andthe output of an ordinary pixel by means of an external circuit asdescribed above.

(6th Embodiment)

FIG. 10 is a schematic circuit diagram of the sixth embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration. In FIG. 10, the circuit configuration of the sensor isillustrated in a simplified form if compared with FIG. 1. It will beappreciated that 25 pixels are arranged in the form of a matrix of 5rows and 5 columns. Two rows of insensitive pixels 2 are arranged inthis embodiment.

FIG. 11 is timing chart illustrating the method of driving the sixthembodiment of infrared sensor. The threshold information is read inperiod 103 shown on the top line for selecting an insensitive pixel rowand the insensitive pixel output is obtained in period 105 shown on thesecond line also for selecting an insensitive pixel row. A high voltageis applied to the source of the amplifier transistor 10 during thethreshold information read period and a low voltage is applied to thesource during the periods 105, 101 for amplifying and reading the pixeloutput signal.

With this embodiment, it is possible to read the threshold value bymeans of the selected insensitive pixel and also read the insensitivepixel output to eliminate the variance of the threshold value of theamplifier transistor 10 and the reset noise of the coupling capacitor11. Additionally, it is possible to use a simple shift register circuitfor the row selection circuit 40 to simplify the design of theperipheral circuits.

(7th Embodiment)

With the arrangement of FIG. 7, a storage/retaining means 311 forholding the output signal obtained on the basis of the retainedinsensitive row information for a frame period and a correction means312 for correcting the effective output signal on the basis of theretained/stored information need to be provided. Furthermore, theembodiment is apt to be influenced by the leak current of the couplingcapacitor 11 and that of the transistor connected to the couplingcapacitor 11 because the coupling capacitor 11 is adapted to store thethreshold information for a frame period. Then, if the leak currents arelarge, the retained threshold information can be changed within a frameperiod to give rise to a longitudinal shading phenomenon on the outputimage. The seventh embodiment and the following embodiments are providedwith means for avoiding this problem.

FIG. 12 is a schematic circuit diagram of the seventh embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration. As shown, the embodiment comprises pixels arranged inthree rows and two columns. In FIG. 12, the components same as orsimilar to those of the embodiment of FIG. 1 are denoted respectively bythe same reference symbols and will not be described any further. Whilepixels are arranged in three rows and two columns in FIG. 12 for thepurpose of simplification, it may be needless to say that the embodimentcan comprise more pixels arranged in the form of a matrix of m rows andn columns.

In FIG. 12, thermoelectric conversion pixels 1 are arranged in the uppertwo rows and insensitive pixels 201 are arranged in the bottom row toform an insensitive pixel row 200. The imaging region 3 includes aregion where the thermoelectric conversion pixels 1 for convertingincident infrared rays into an electric signal are two-dimensionallyarranged and a region of the insensitive pixel row 200 of insensitivepixels 201.

The configuration of the thermoelectric conversion pixels 1 is same asthat of FIG. 2. The configuration of the insensitive pixels 201 issimilar to FIG. 2, but without having the cavity structure. While theinsensitive pixel row 200 is arranged below the thermoelectricconversion pixel rows in FIG. 12, it may alternatively be arranged abovethe thermoelectric conversion pixel rows, if necessary. While at least asingle insensitive pixel row has to be provided, two or more than twoinsensitive pixel rows may alternatively be provided, if appropriate.

Row selection lines 4 (4-1, 4-2, 4-3) and vertical signal lines 5 (5-1,5-2) are arranged in the imaging region 3. The row selection lines 4 areconnected to the row selection circuit 40 for selecting a row and drivento select for that purpose. The vertical signal lines 5 are connected toa constant current source for supplying a bias current to be used forreading a signal from a thermoelectric conversion pixel 1 or aninsensitive pixel 201.

A first coupling capacitor 11 is arranged between each of the verticalsignal lines 5 and the gate of the corresponding one of the amplifiertransistors 10 (10-1, 10-2) and a sampling transistor 15 is arrangedbetween the gate and the drain of each of the amplifier transistors 10in order to bypass the problem attributable to the variance of thethreshold voltage of the amplifier transistors 10 as in the case of FIG.1. However, the circuit configuration of FIG. 12 differs from that ofFIG. 1 in terms of the amplifying/read circuit and the downstreamcircuits. The drain of each of the amplifier transistors 10 is connectedto a second coupling capacitor 33 by way of an integrating transistor(INT) 32 arranged on each column. The other end of each of the secondcoupling capacitors 33 is connected to a storage capacitor 30 and alsoto a clamp transistor (CL) 31. The signal voltages stored and retainedin the storage capacitors 30 are sequentially reads by the horizontalselection circuit 6 to the output section 24 by way of the horizontalread transistors 61, 62 on a time series basis.

With the arrangement of FIG. 12, the threshold voltage information ofthe amplifier transistors 10 is sampled in each horizontal scanningperiod so that the duration of holding the threshold voltage informationof the coupling capacitors can be reduced to that of the horizontalscanning period. Thus, the influence of the leak currents of couplingcapacitors 11 and the sampling transistors 15 connected thereto can beremarkably reduced.

For example, the threshold voltage holding period of the couplingcapacitor 11 is equal to a frame period with the arrangement of FIG. 1.Therefore, there is a risk of producing a vertical shading phenomenondue to the influence of such leak currents. Additionally, more seriousvertical shading problems can arise and the image operation can becomeimpossible from a certain row if the level of such leak currents israised due to variances in the manufacturing process. In other words, along threshold voltage holding period can give rise to problems in fromthe viewpoint of both stability of sensor performance and that ofmanufacturing process.

To the contrary, with this embodiment, since the threshold voltage issampled in each horizontal scanning period so that the above describedvertical shading problem does not arise. Additionally, since theduration of holding the threshold voltage is reduced greatly from aframe period to a horizontal scanning period, the specification for thepurpose of prevention of leak current is allowed to be by far lessrigorous to by turn improve the stability of manufacturing process andhence infrared sensors according to the invention can be manufactured ona stable and reliable basis.

Furthermore, with the arrangement of FIG. 12, the difference between theoutput voltage of the selected thermoelectric conversion pixel 1 andthat of the selected insensitive pixel 2 can be determined for everyhorizontal scanning period. This means that the two types of noise asdescribed below can be reduced and hence the manufacturing yield can beimproved because of the effect of suppressing such noises. One is thereset noise that appears in the operation of sampling the thresholdvoltage information of the amplifier transistor 10. With thisembodiment, this type of noise can be eliminated inside the columnamplifying/read circuit. The reset noise of the coupling capacitor 11can be estimated in a manner as described below.

The reset noise voltage is expressed by Vn=(kT/C)^(1/2), where k is theBoltzmann constant and T is the absolute temperature. Therefore, if thecoupling capacitance is assumed to be equal to 1 pF, the reset noisethat is generated in the coupling-capacitor is as large as about 60 ìV.If the above described estimated infrared sensitivity is applied, theabove value refers to 1.2[K] when reduced to the temperature of theobject of imaging. Therefore, the reset noise can be a very large noisecomponent. Thus, in order to realize a high sensitivity sensor, it isindispensably necessary to remove the reset noise of the couplingcapacitor by any means. FIG. 7 illustrates an arrangement for removingthe reset noise.

FIG. 13 is a timing chart illustrating the method of driving the seventhembodiment of infrared sensor. Now, the operation of the infrared sensorof FIG. 12 will be described by referring to the timing chart of FIG.13. An operation of sampling the threshold voltage of an amplifiertransistor 10 (period a in FIG. 13), an operation of reading the signalof an insensitive pixel 201 (period b in FIG. 13) and an operation ofreading the signal of a thermoelectric conversion pixel 1 (period c inFIG. 3) take place in horizontal blanking period 301.

Firstly, all the row selection lines 4 are held off so that the rowselection circuit 40 is held in a non-selection state and hence does notperform any row selecting operation. Therefore, as described above, thesubstrate potential Vs that is applied as the source voltage of the loadMOS transistors 8 appears on the vertical signal lines 5. Then, thesampling transistors 15 and the reset transistors 13 are turned on. As aresult, the gate 10 g and the drain 10 d of each of the amplifiertransistors 10 show a same voltage level and reset by the correspondingreset transistor 15. Thus, both of the amplifier transistors 10 arebrought into an on state.

Then, as the reset transistors 13 are turned off, the drain voltage andthe gate voltage of each of the amplifier transistors 10 fall due to thedrain current until the drain current becomes equal to 0. The drainvoltage and the gate voltage of each of the amplifier transistors 10under this condition represent the threshold voltage of the amplifiertransistor 10. Thereafter, as the sampling transistors 15 are turnedoff, the gate and the drain of each of the amplifier transistors 10 areisolated from each other, from then on, each of the sampled thresholdvoltages is held to the first coupling capacitor 11 of the correspondingcolumn.

Subsequently, the reset transistors 13, the integrating transistors 32and the clamp transistors 31 are turned on. At this time, the drainvoltage of each of the amplifier transistor 10 and the voltage of eachof the second coupling capacitors 33 are reset and the voltage Vcs ofeach of the storage capacitors 30 is fixed to a desired voltage level.

Then, the reset transistors 13 are turned off and the gate modulationintegration circuit starts an amplifying/read operation. The supplyvoltage Vd is applied to the row selection line 4-3 by the row selectioncircuit 40 to select an insensitive pixel of the insensitive pixel row200. At this time, the selected insensitive pixel 201 of the insensitivepixel row 200 is forwardly biased by the corresponding load MOStransistor 8 by way of the corresponding vertical signal line 5 so thatthe operation point of each of the pn junctions in the inside of theinsensitive pixel 2 is determined by the forward bias current that isdetermined by the load MOS transistor 8 and the temperature of thesemiconductor substrate 17 and the insensitive pixel output is producedto the vertical signal line 5. The voltage change produced in thevertical signal line 5 modulates the gate voltage of the correspondingamplifier transistor 10 by way of the coupling capacitor 11 to turn onthe amplifier transistor 10 so that a drain current flows and stored inthe second coupling capacitor 33.

Then, as the selection of the row selection line 4-3 by the rowselection circuit 40 is terminated to turn off the amplifier transistor10 and complete the operation of reading the integrated gate modulation.The signal output of the insensitive pixel 201 is stored in the secondcoupling capacitor 33. After turning off the clamp transistor 31, thereset transistor 13 is turned on and the drain voltage of the amplifiertransistor 10 and the voltage of the second coupling capacitor 33 arereset. The reset transistor 13 is turned off again.

Subsequently, the supply voltage Vd is applied to the row selection line4-1 by the row selection circuit 40 to select a thermoelectricconversion pixel of the first row. At this time, the selectedthermoelectric conversion pixel 1 of the first row is forwardly biasedby the corresponding load MOS transistor 8 by way of the correspondingvertical signal line 5 so that the operation point of each of the pnjunctions in the inside of the thermoelectric conversion pixel 1 isdetermined by the forward bias current that is determined by the loadMOS transistor 8 and the temperature of the semiconductor substrate 17and the thermoelectric conversion pixel output of the first row isproduced to the vertical signal line 5. An operation of reading theintegrated gate modulation by means of the thermoelectric conversionpixel output is conducted in a manner similar to the operation of therow selection circuit 40 for selecting the first row in the period(period c of FIG. 13) or that of the operation for selecting theinsensitive pixel row in the above described insensitive pixel rowselection period (period b in FIG. 13). As a result, the drain currentis stored in the second coupling capacitor 33 as signal charge. Sincethe clamp transistor 31 is off at this time, the voltage Vcs of thestorage capacitor 30 is modulated by the signal charged produced by theabove thermoelectric conversion pixel.

Finally, as the integrating transistor 32 is turned off, the operationfor the first row in the horizontal blanking period is completed. Atthis time, the storage capacitor 30 retains the voltage Vcs that ismodulated by the difference between the output of the insensitive pixel201 and the thermoelectric conversion pixel 1 by referring to the clampvoltage that is held to a fixed level by the operation of turning on theclamp transistor 31.

Then, in the horizontal readout period 300, the horizontal readtransistors 61, 62 are sequentially turned on by the horizontalselection circuit 70 and their outputs signals are read out to theoutput line 24 on a time series basis. The operation in the subsequenthorizontal blanking period 302 is basically identical with the operationin the above described horizontal blanking period 301 except that therow selection line selected by the row selection circuit 40 is not thefirst row selection line 4-1 but the second row selection line 4-2.Subsequently, in the horizontal readout period 300 that follows thehorizontal blanking period 302, the horizontal read transistors 61, 62are sequentially turned on by the horizontal selection circuit 70 andtheir output signals are read out to the output line 24 on a time seriesbasis as in the case of the operation of reading the output signals ofthe first row.

With the above described operations, it is possible to sample thethreshold value of the amplifier transistor 10 in each and everyhorizontal scanning period as described above so that low noise infraredsensors that are resistant against variances in the manufacturingprocess can be manufactured at a high yield. Additionally, unlike thearrangement of FIG. 7, no external circuits such as a memory means 311and a correction means need to be provided so that all the componentscan be arranged on a chip and hence the infrared sensor can be preparedat low cost.

While there may be a number of different timing charts other than theone shown in FIG. 13 that can be used for driving the embodiment of FIG.12, the timing chart of FIG. 14 that is adapted to drive the source ofthe amplifier transistor 10 by means of a pulse voltage will bedescribed below. FIG. 14 is basically identical with FIG. 13 for themost part in terms of operations. However, FIG. 14 uses a pulse drivetype voltage for the source SS of the amplifier transistor instead ofthe DC drive type voltage of FIG. 13. Beside, a pulse is also applied tothe row selection line 4-3 for the insensitive pixel row 200 at a timingsynchronized with the application of the pulse voltage. Since theoperations of FIG. 14 are basically same as those of FIG. 13, the sameparts will not be described any further.

According to FIG. 14, as an operation for sampling the threshold voltageof the amplifier transistor 10 in the initial stages of the horizontalblanking period 301 (period a of FIG. 14), a pulse voltage Vs is appliedto the source SS. At the same time the row selection line 4-3 forselecting the insensitive pixel row 200 is turned on. As a result, sincethe source SS of the amplifier transistor 10 is brought to a voltagelevel higher than that of the substrate voltage Vs, the sampledthreshold voltage is the one observed when the source SS of theamplifier transistor 10 shows the voltage of Vs so that a thresholdvoltage higher than its counterpart of FIG. 13 is sampled. Thus, thesource SS is held to the substrate voltage Vs in the subsequentoperations including the operation from the selection of the insensitivepixel row 200 to the reading of the integrated gate modulation a is atiming chart illustrating the method of driving the eighth embodiment ofinfrared sensor and the operation from the selection of a thermoelectricconversion pixel row to the reading of the integrated gate modulation.

With the timing chart of FIG. 14, the operation points of the amplifiertransistor 10 to be regulated is increased to make it possible tooperate the related elements in a more optimal condition. Consequently,the infrared sensor can operate with a higher sensitivity. In the caseof the timing chart of FIG. 13, the operation point of the amplifiertransistor 10 is determined by the supply voltage Vd applied to the rowselection line by the row selection circuit 40. However, since thesupply voltage Vd applied by the row selection circuit 40 also affectsthe sensitivity of the thermoelectric conversion pixels 1, it will notbe allowed to simply optimize the operation of the amplifier transistor10 depending on the circumstances. In other words, the amplificationfactor of the amplifier transistor 10 may not necessarily be optimizedand hence the sensitivity of the thermoelectric conversion pixels 1 maynot necessarily be maximized.

While the signal output from the insensitive pixel 201 is read out andsubsequently the signal output from the thermoelectric conversion pixel1 is read out according to the timing charts of FIGS. 13 and 14, it isalso possible to read the signal output from the thermoelectricconversion pixel 1 and subsequently the signal output from theinsensitive pixel 201. Furthermore, the timing charts of FIGS. 13 and 14are designed to determine the difference between the thermoelectricconversion pixel 1 and the insensitive pixel 201, it is also possible todetermine the difference of the outputs of two thermoelectric conversionpixels belonging to different rows. Such an arrangement provides anadvantage of determining the difference of the outputs of twothermoelectric conversion pixels belonging to adjacently located rows inaddition to all the above described advantages. Then, it is possible toprovide a so-called edge detecting features, although the feature may belimited to a vertical direction.

(8th Embodiment)

FIG. 15 is a schematic circuit diagram of the eighth embodiment ofinfrared sensor according to the invention, illustrating its entireconfiguration. Pixels are arranged in the form of a 3×2 matrix, wherethermoelectric conversion pixels 1 are arranged in the upper two rowsand insensitive pixels 201 are arranged in the bottom row to form aninsensitive pixel row 200.

The imaging region 3 includes a region where the thermoelectricconversion pixels 1 for converting incident infrared rays into anelectric signal are two-dimensionally arranged and a region of theinsensitive pixel row 200 of insensitive pixels 201. The configurationof the thermoelectric conversion pixels 1 is same as that describedabove by referring to FIG. 2. The configuration of the insensitive pixel201 is similar to FIG. 2 but without having the cavity structure. Thusthe insensitive pixel 201 is thermally insensitive. Since thearrangement of FIG. 15 is basically same as that of FIG. 12 illustratingthe seventh embodiment, the eighth embodiment will be described only interms of the difference between it and the seventh embodiment.

The imaging region 3, its peripheral circuits, the gate modulationintegration circuit connected thereto by way of the vertical signallines 5-1, 5-2 and the first coupling capacitors 11 and the circuit forprocessing the difference of the outcomes of the two signal readingoperations are configured same as their respective counterparts of FIG.12. This embodiment is additionally provided with a sample-and-holdcircuit between each of the first storage capacitor 30 and thecorresponding horizontal read transistor 14.

Thus, the signal voltage held to each of the first storage capacitors 30is fed to the corresponding second storage capacitor 43 connected to itby way of a transfer transistor 42. The horizontal selection transistors61, 62 are adapted to sequentially read the signals stored in the secondstorage capacitors 43. A second reset transistor 44 is connected to eachof the second storage capacitors 43 in order to initialize the voltageof the second storage capacitor 43. By separating the first storagecapacitors 30 and the second storage capacitors 43 by means of transfertransistors 42, it is possible to read the integrated gate modulation byusing the first storage capacitors 30 under a condition where the signalvoltage is held to the second storage capacitors 43.

FIG. 16 is a timing chart illustrating the method of driving the eighthembodiment of infrared sensor shown in FIG. 15. The operation of theembodiment will be described below.

The operation of this embodiment differs from that of the seventhembodiment in that the operation of reading the image pickup signalconducted in horizontal blanking periods 101, 102 in the seventhembodiment is conducted in horizontal readout periods 100. Operationssimilar those in the horizontal blanking period shown in FIG. 13 areconducted in the first horizontal readout period 100. They include anoperation of sampling the threshold voltage of the amplifier transistor10 in each and every horizontal scanning period (period a in FIG. 16),an operation of reading the integrated gate amplification of the darksignal from the insensitive pixel 201 under a condition where thevoltage of the first storage capacitor 30 is fixed (period b in FIG. 16)and an operation of reading the integrated gate amplification of thelight signal from the thermoelectric conversion pixel of the selectedrow that is conducted after turning off the clamp transistor 31 forprocessing differences (period c in FIG. 16). Consequently, theinfluence of the variance of the threshold value of the amplifiertransistor 10 is eliminated from the first storage capacitor 30 and alow noise signal voltage is held by the first storage capacitor 30 undera condition where the 1/f noise of the load MOS transistor 8 and that ofthe amplifier transistor 10 are lowered as a result of limiting thesignal bandwidth in a low frequency zone.

The transfer transistor 42 is held off and the horizontal readtransistor 14 is isolated from the first storage transistor 30. Whilethe horizontal selection transistors 61, 62 are sequentially selected bythe horizontal pulse from the horizontal selection circuit 70, a resetsignal is output to the output section 24.

Only an operation of transferring the signal voltage stored in the firststorage capacitor 30 to the second storage capacitor 43 is performed inthe horizontal blanking period 101 of this embodiment (period d in FIG.16). Firstly, the second reset transistor 44 is turned on while thevoltage of the second storage capacitor 43 is reset and the second resettransistor 44 is turned off again. Subsequently, the transfer transistor42 is turned on while the signal charge held to the first storagecapacitor 30 is transferred to the second storage capacitor 43 and thetransfer transistor 42 is turned off again. The signal voltagestransferred to second storage capacitor 43 in this horizontal blankingperiod 101 are sequentially read out in the next horizontal readoutperiod (period c in FIG. 16).

With this embodiment, it is possible to carry out the operation ofreading the integrated gate modulation from the insensitive pixel 201and that of reading the integrated gate modulation from thethermoelectric conversion pixel 1 in an effective period that takes mostof a horizontal scanning period. In other words, the width of the rowselection pulse that dominates the above operation of reading theintegrated gate modulation can be expanded to a large extent. As aresult, it is possible to limit the signal frequency band side at thehigh frequency side and hence reduce random noise. Therefore, it ispossible to realize an even low noise infrared sensor. Of course, thisembodiment also provides the advantages of the seventh embodimentincluding that of reducing 1/f noise that can appear in the load MOStransistor and the amplifier transistor due to the limited signalfrequency band at the low frequency band side, that of preventing thephenomenon of vertical shading attributable to sampling the thresholdvoltage in every horizontal scanning period from occurring and that ofeliminating high level reset noise that can appear in the first couplingcapacitor 11.

Since the resistance against variances in the manufacturing process isimproved by these advantages, infrared sensors can be manufactured at ahigh yield on a stable basis if the manufacturing process involvesvariances as in the case of the seventh embodiment.

The infrared sensor of FIG. 15 can be driven by using various timingcharts other than the one shown in FIG. 16. FIG. 17 is a timing chartillustrating a technique of driving the source of the amplifiertransistor 10 by means of a pulse voltage. The operation using thetiming chart of FIG. 17 is basically same as the one using the timingchart of FIG. 16. They are same and identical for the most part. While aDC voltage is used for driving the source of the amplifier transistor 10in FIG. 16, a pulse voltage is used for driving the source of theamplifier transistor 10 in FIG. 17. Additionally, a pulse is added tothe row selection line 4-3 of the insensitive pixel row 200 at thesynchronized timing.

Since the operation of FIG. 17 is basically same and identical with thatof FIG. 16, the same parts will not be described any further. With theoperation of FIG. 17, a pulse voltage Vs is applied to the source SS ofthe amplifier transistor 10 for the purpose of sampling the thresholdvoltage of the amplifier transistor 10 in an initial part of theeffective period 100 (period a in FIG. 17) and at the same time the rowselection line 403 for selecting the insensitive pixel row 200 is turnedon. Since the source SS of the amplifier transistor 10 is held to avoltage level higher than that of the substrate voltage Vs for thisoperation, the sampled threshold voltage is the one obtained when thesource SS of the amplifier transistor 10 is at Vs. In other words, athreshold voltage higher than its counterpart of FIG. 16 is sampled. Inthe operation of reading the integrated gate modulation from theselected insensitive pixel row and that of reading integrated gatemodulation form the selected thermoelectric conversion pixel row thattake place subsequently, the source SS is set to the substrate voltageVs.

With the technique of driving the embodiment, the object of regulationof the operation point of the amplifier transistor 10 is expanded tomake it possible to drive the related elements in a more optimal stateto consequently realize an improved sensitivity for the infrared sensor.More specifically, in the instance of FIG. 16, the operation point ofthe amplifier transistor 10 is determined by the supply voltage Vdapplied to the row selection line by the row selection circuit 40.However, since the supply voltageVd applied by the row selection circuit40 can also affect the sensitivity of the thermoelectric conversionpixel 1, it is not allowed to optimize only the operation of theamplifier transistor 10. The amplification factor of the amplifiertransistor 10 may not necessarily be optimized and hence the sensitivityof the thermoelectric conversion pixels 1 may not necessarily bemaximized.

While the signal output from the insensitive pixel 201 is read out andsubsequently the signal output from the thermoelectric conversion pixel1 is read out according to the timing charts of FIGS. 16 and 17, it isalso possible to read the signal output from the thermoelectricconversion pixel 1 and subsequently the signal output from theinsensitive pixel 201. Furthermore, the timing charts of FIGS. 16 and 17are designed to determine the difference between the thermoelectricconversion pixel 1 and the insensitive pixel 201, it is also possible todetermine the difference of the outputs of two thermoelectric conversionpixels belonging to different rows. Such an arrangement provides anadvantage of determining the difference of the outputs of twothermoelectric conversion pixels belonging to adjacently located rows inaddition to all the above described advantages. Then, it is possible toprovide a so-called edge detecting features, although the feature may belimited to a vertical direction.

(9th Embodiment)

FIG. 18 s a schematic circuit diagram of the ninth and tenth embodimentsof infrared sensor according to the invention, illustrating its entireconfiguration. Pixels are arranged in the form of an m×n matrix (where mand n are natural numbers not smaller than 2).

Infrared sensing thermoelectric conversion pixels 1 for convertingincident infrared rays into an electric signal are arrangedtwo-dimensionally on a semiconductor substrate 2 to form an imagingregion 3. Row selection lines 4 (4-1, 4-2, . . . ), or horizontalselection lines, and vertical column selection lines 5 (5-1, 5-2, . . .), or vertical selection lines, are arranged in the imaging region 3. Arow selection circuit 40 and a column selection circuit 70 arerespectively arranged adjacent to these lines in the row direction andin the column direction of the imaging region 3 and connected to the rowselection lines 4 and the column selection lines 7, or the horizontalselection lines.

The row signal lines 5 are connected to respective load MOS transistors8-1, 8-2 operating as constant current sources 80 for obtaining a pixeloutput voltage.

In FIG. 18, the substrate voltage:Vs is applied to the sources of theload MOS transistors. Preferably, the source voltage can be regulated.

The supply voltage:Vd is applied to the row selection line 4 selected bythe row selection circuit 40, which may be the row selection line 4-1for example, while Vs is applied to all the row selection linesunselected by the row selection circuit 40. As a result, the regions ofpn junctions 115 in the inside of the thermoelectric conversion pixels 1of the selected row 4-1 are forwardly biased to flow a bias current sothat the operation point is determined in each pixel by the temperatureof the pn junctions in the inside of the pixel and the forward biascurrent. Consequently, a pixel signal output voltage is produced in eachof the column signal lines 5-1, 5-2, . . . . At this time, the regionsof pn junctions 115 a, . . . of the pixels not selected by the selectioncircuit 40 are reversely biased. In other words, the pn junctions in theinside of each pixel have a pixel selecting function.

The voltage generated in the vertical signal lines 5 is a very lowvoltage. Assume that the ratio of the temperature change of the objectof imaging is dTs to the temperature change of the pixel dTd is 5×10⁻³.Then, it will be appreciated that the voltage generated in the verticalsignal lines 5 is as low as 5 [ìV] form this value and thethermoelectric conversion sensitivity dv/dTd=10 [mV/K] that is obtainedwhen the eight pn junctions of the pixels are connected in series.

Therefore, in order to recognize this temperature difference on theobject of imaging, the noise that is generated in the vertical signallines 5 needs to be made lower than 5 [ìV]. This noise level is as lowas about {fraction (1/80)} of the noise of a CMOS sensor that is usedfor a MOS type visible light image sensor.

A column amplifying circuit 9 is arranged between the signal lines 5-1,5-1, . . . and the column selection transistor group 60 and the gates 10g of the amplifying MOS transistors 10 of the amplifying circuit 9 areconnected to the respective signal lines. A storage capacitor 12 isconnected to the drain 10 d of each of the MOS transistors 10 for thepurpose of integrating and storing the amplified signal current. Thestorage time to be used for integrating the signal current is determinedby the row selection pulse applied to the row selection line 4 from therow selection circuit 40.

The storage capacitor 12 is connected to a reset transistor forresetting the voltage of the storage capacitor 12 and reset after thecompletion of the operation by the column selection transistor 6 ofreading the signal voltage. Terminal 24 in FIG. 18 is an outputterminal.

The infrared sensing thermoelectric conversion pixels 1 of thisembodiment have a structure as described above by referring to FIG. 2.

The ninth embodiment of the invention comprises a voltage generator 320mounted on the semiconductor substrate as shown in FIG. 18. The voltagegenerator 320 is connected to the row selection circuit 40 by way ofterminal 21. As a row selection pulse is input to the voltage generator320, it generates a ramp waveform voltage that is synchronized with therow selection pulse as shown in FIG. 19 in a row selection period andsupplies it to the sources 10 s of the amplifier transistors 10 in thecolumn amplifying circuit 9 as source voltage.

FIG. 26 shows the temperature rise due to self heating of a pixel asdescribed earlier. The thermal time constant of this temperature rise isdetermined by the heat isolation of the thermoelectric conversion pixel1 and normally has a magnitude of about [ms].

On the other hand, a row selection period is of the order of [ìs] asillustrated in FIG. 26 and hence very short if compared with the thermaltime constant. Therefore, linear approximation can be allowed with awide margin during a row selection period. Thus, the voltageattributable to self heating generated in the column signal line andapplied to the gate 10 g of the amplifier transistor 10 can be offset bythe ramp waveform voltage applied to the source 10 s of the amplifiertransistor 10 and only the signal of the temperature change due to theincident infrared rays can be amplified.

As a result, it is possible to optimize the operation point of theamplifier transistor 10 and amplify the current of only the signalcomponent by eliminating the self heating component. Thus, it is nowpossible to improve the gain and random noise attributable to anexpanded band will not be increased undesirably. Therefore, it possibleto provide an uncooled type infrared sensor that has a broad dynamicrange.

(10th Embodiment)

In FIG. 18, a voltage generator 320 for generating a step waveformvoltage is mounted on the semiconductor substrate. As a row selectionpulse is input from the row selection circuit 40 to the voltagegenerator 320, it generates a step waveform voltage that is synchronizedwith the row selection pulse as shown in FIG. 19 and supplies it to thesources 10 s of the amplifier transistors 10 in the row amplifyingcircuit 9 as source voltage, or the second input.

A D/A converter circuit may be used for generating a step waveformvoltage. An effect practically same as that of applying a ramp waveformvoltage can be obtained when a step waveform voltage is used providedthat the number of bits is appropriately selected. Additionally, the useof a step waveform voltage provides an advantage that the waveform linecan be regulated finely.

Therefore, as in the case of the ninth embodiment, the voltageattributable to self heating generated in the column signal line andapplied to the gate 10 g of the amplifier transistor 10 can be offset bythe ramp waveform voltage applied to the source 10 s of the amplifiertransistor 10 and only the signal of the temperature change due to theincident infrared rays can be amplified.

As a result, it is possible to optimize the operation point of theamplifier transistor 10 and amplify the current of only the signalcomponent by eliminating the self heating component. Thus, it is nowpossible to improve the gain and random noise attributable to anexpanded band will not be increased undesirably. Therefore, it possibleto provide an uncooled type infrared sensor that has a broad dynamicrange.

Either of the ninth embodiment or the tenth embodiment can be modifiedin such a way that the voltage generator 320 is arranged outside thesemiconductor substrate. As a row selection pulse is input from the rowselection circuit 40 to the voltage generator 320, the voltage generator320 generates a ramp waveform voltage or a step waveform voltage that issynchronized with the row selection pulse as shown information FIG. 19or FIG. 20 and supplies it to source voltage input section 22 arrangedon the semiconductor substrate by way of wire 23 and further to thesources 10 s of the amplifier transistors 10 in the row amplifyingcircuit 9 as source voltage.

Therefore like the ninth embodiment and the tenth embodiment, thevoltage attributable to self heating generated in the column signal lineand applied to the gate 10 g of the amplifier transistor 10 can beoffset by the ramp waveform voltage applied to the source 10 s of theamplifier transistor 10 and only the signal of the temperature changedue to the incident infrared rays can be amplified.

As a result, it is possible to optimize the operation point of theamplifier transistor 10 and amplify the current of only the signalcomponent by eliminating the self heating component. Thus, it is nowpossible to improve the gain and random noise attributable to anexpanded band will not be increased undesirably. Therefore, it possibleto provide an uncooled type infrared sensor that has a broad dynamicrange.

(11th Embodiment)

FIGS. 21 and 22 illustrate the eleventh embodiment. In FIGS. 21 and 22,the components same as those of FIG. 18 are denoted respectively by thesame reference symbols. The embodiment has a configuration similar tothat of FIG. 18 except that the voltage generator 321 is adapted togenerate a rectangular waveform voltage and an integration circuit 322is arranged between the voltage generator 321 and the source voltageinput terminals 22 of the amplifier transistors. The voltage generator321 is mounted on the semiconductor substrate. As a row selection pulsefrom the row selection circuit 40 is input to the voltage generator 320by way of the row selection pulse output section 21, the voltagegenerator 321 generates a rectangular waveform voltage V1 that issynchronized with the row selection pulse ((a) in FIG. 22).

As pointed out above, an integration circuit 322 containing an electriccapacitor 323 is arranged on the wire 23 extending between the voltagegenerator 321 and the amplifier transistor source voltage input section22 on the semiconductor substrate. As shown in (a) of FIG. 22, as arectangular waveform voltage V1 that is synchronized with the rowselection pulse is input to the integration circuit 322, the latterproduces an integrated waveform voltage V2 as shown in (b) of FIG. 22and supplies it to the amplifier transistor source voltage input section22 on the sensor chip as source voltage of the amplifier transistor 10in the column amplifying circuit 9. This integrated ramp waveform can beapproximated to the voltage component attributable to self heating thatis contained in the input signal of the amplifier transistor. Thus, thevoltage component of self heating that is generated on the column signalline and applied to the gate 10 g of the amplifier transistor 10 can beoffset by the integrated waveform voltage applied to the source of theamplifier transistor 10 as in the case of the first and secondembodiments to make it possible to amplify only the signal representingthe temperature change due to incident infrared rays.

As a result, it is possible to optimize the operation point of theamplifier transistor 10 and amplify the current of only the signalcomponent by eliminating the self heating component. Thus, it is nowpossible to improve the gain and random noise attributable to anexpanded band will not be increased undesirably.

The eleventh embodiment may be modified in such a way that the voltagegenerator 321 and the integration circuit 322 are arranged outside thesensor chip.

(12th Embodiment)

FIGS. 23 and 24 illustrate the twelfth embodiment. In FIGS. 23 and 24,the components same as those of FIG. 18 are denoted respectively by thesame reference symbols. In this embodiment, the pixels of every otherrows are grouped to form two groups of pixels including a pixel group ofodd number rows and that of even number rows and the voltage generator324 of the first group and the voltage generator 325 of the secondgenerator are operated alternately. In this embodiment, asample-and-hold (S/H) circuit of a 1H period is added for the purpose ofreducing random noise and most of the 1H period is used as row selectionperiod, or a pixel selection period.

It is also possible to provide a circuit configuration and a drivemethod by which the signal charge accumulated by the column amplifyingoperation is moved to the added sample-and-hold circuit and output at atiming delayed by a time period corresponding to a row. If such is thecase, all the rows are processed by a same circuit and hence thegeneration of noise of a fixed pattern such as a pattern of horizontalstripes corresponding to every other rows can be effectively suppressedto a great advantage.

When such a drive method is used, the non-selection period t1 of pixelselection pulses of two consecutive rows can be very short depending onthe time constant selected on the basis of the added capacity. Then, thevoltage Vs′ of the amplifier transistor source voltage input section onthe semiconductor substrate may not fall sufficiently as compared with adesired fall indicated by Vs″ in FIG. 24. The infrared sensor may notoperate properly under such a condition.

To bypass the above identified problem, two voltage generators 324, 325corresponding to the two groups of pixels are provided along with twoamplifier transistor source voltage input sections 22 so that everyother rows of pixels maybe selected sequentially by switching. With thisarrangement of two voltage generators 324, 325, voltages Vs, Vs havingrespective waveforms shown in (b) and (c) in FIG. 24 are outputalternately and, at the same time, the voltages Vs, Vs shown in (b) and(c) are supplied in the inside of the sensor chip as source voltage ofthe amplifier transistor in the column amplifying/read circuit 90.

Thus, as in the case of the ninth through eleventh embodiments, thevoltage attributable to self heating generated in the column signal lineand applied to the gate 10 g of the amplifier transistor 10 can beoffset by the ramp waveform voltage applied to the source 10 s of theamplifier transistor 10 and only the signal of the temperature changedue to the incident infrared rays can be amplified.

As a result, it is possible to optimize the operation point of theamplifier transistor 10 and amplify the current of only the signalcomponent by eliminating the self heating component. Thus, it is nowpossible to improve the gain and random noise attributable to anexpanded band will not be increased undesirably. Therefore, it possibleto provide an uncooled type infrared sensor that has a broad dynamicrange.

(13th Embodiment)

The thirteenth embodiment of the invention will be described byreferring to FIGS. 25 and 6. The thermoelectric conversion pixels 1 ofthis embodiment have cavity support structure for supporting pn junctionregions as described earlier by referring to FIGS. 2A and 2B and thearrangement of a constant current source 80 realized by using loadtransistors, a row selection circuit 40, row selection lines 4, columnselection circuit 70, column signal lines 5, a column selectiontransistor group 60 and a column amplifying/read circuit 90 is same asthat of FIG. 18 and hence will not be described any further.

In this embodiment, a thermally isolated insensitive pixel column 500 isprovided as the last column as shown in FIG. 25 in such a way that eachrow is provided with a thermally isolated insensitive pixel 501 having astructure same as the one illustrated in FIG. 6. Note that eachthermally isolated insensitive pixel 501 has a structure same as thepixel 201 illustrated in FIG. 6. In the thermally isolated insensitivepixel 501, incident infrared rays are reflected by the infraredreflection layer 130 and no temperature change occurs if the pixel isstricken by infrared ray so that it only outputs a self heating signalthat is generated when it is selected to the column signal line 502. Thecolumn amplifying read circuit 90 is connected to the column signallines by way of a respective coupling capacitors 11.

With this arrangement, it is possible to obtain the output of thethermally isolated insensitive pixel row 500 by way of the column signalline and the coupling capacitor 11 and supply it as source voltage tothe source of the amplifier transistors 19 in the column amplifying readcircuit 90 (see FIG. 18) by way of a source follower circuit 400 asshown in FIG. 25.

As for the regulation of operation point, the operation point of eachpixel can be optimized by regulating the voltages of the terminals 401,402 of the source follower circuit. Therefore, as in the case of the 9ththrough the 12th embodiments, the voltage attributable to self heatingthat is generated in the column signal line 5 outputting a signal can beaccurately offset by applying the waveform voltage of the column signalline to the source input section 22 of the amplifier transistors 10 andonly the signal of the temperature change due to the incident infraredrays can be amplified. Since the voltage component attributable to selfheating always show a same profile, the waveform obtained by mountinginsensitive pixels on the same semiconductor substrate can be utilizedto offset the voltage component.

As a result, it is possible to optimize the operation point of theamplifier transistor 10 and amplify the current of only the signalcomponent by eliminating the self heating component. Thus, it is nowpossible to improve the gain and random noise attributable to anexpanded band will not be increased undesirably. Therefore, it possibleto provide an uncooled type infrared sensor that has a broad dynamicrange.

While the use of a single source follower circuit 400 is described aboveby referring to FIG. 25, it may be replaced by a plurality of sourcefollower circuits 400 if necessary.

Additionally, the circuit 400 is not limited to a source followercircuit and may be replaced by any appropriate circuit that provides thesame effect without affecting the output voltage of the column signalline of the thermally isolated insensitive pixel row.

The present invention is described above in terms of the use of a columnamplifying circuit comprising a single amplifier MOS transistor usingthe gate for the first input and the surface for the second input asoutput signal amplifier. The use of such an amplifying circuit isadvantageous from the manufacturing viewpoint because the circuit has asimple configuration. However, other amplifying circuit such as adifferential amplifier may alternatively be used so long as it is of thetwo inputs type.

The thermoelectric conversion pixels of the present invention aredescribed in terms of those having pn junctions. However, the presentinvention is not limited thereto. For example, the present invention isalso applicable to an infrared sensor comprising thermoelectricconversion pixels realized by using a bolometer typically made ofvanadium oxide.

The present invention is by no means limited to the above describedembodiments. The pixel arrangement may be modified in various differentways so long as they are arranged in an m×n matrix. The thermoelectricconversion pixels are not limited to the structure illustrated in FIGS.2A and 2B and may be modified appropriately. In other words, anyarrangement realized by arranging infrared absorption means forabsorbing incident infrared rays and transforming them into heat,thermoelectric means for transforming the heat generated by the infraredabsorption means into an electric signal, pixel selection means forselecting a pixel from which the pixel output signal obtained by thethermoelectric conversion means is read and output means for outputtingthe pixel output signal from the thermoelectric conversion pixelselected by the pixel selection means on a semiconductor substrate fallswithin the scope of the present invention. Additionally, elementsadapted to transform infrared rays directly into an electric signal mayalternatively be used within the scope of the present invention.

Furthermore, the above described embodiments may be modified in variousdifferent ways.

As described above in detail, according to the invention, the signallines where the pixel output appears and the gates of the amplifiertransistors are separated from each other DC-wise by arranging couplingcapacitors between them and each frame is made to hold the thresholdinformation of the amplifier transistors of each column in the gates ofthe amplifier transistors in order to eliminate any variance among thevoltage gains of the columns that can be produced as a result offluctuations of the threshold value of the amplifier transistors, whichmay vary from column to column. Thus, the influence of fluctuations ofthe threshold value of each column can be eliminated to make it nolonger necessary to provide a margin for the operating voltage region ofthe storage capacitors for the purpose of coping with such fluctuationsand securing a voltage swing of the storage capacitors. Therefore,according to the invention, it is possible to design a large gain forthe gate modulation integration circuit so that a highly sensitiveuncooled type infrared sensor can be realized. Additionally, thepotential of the storage capacitor can be fully exploited for the samereason to make it possible to provide an uncooled type infrared sensorhaving a wide dynamic range. Furthermore, the influence of self heatingattributable to the read current of the thermoelectric conversionsection is offset to realize an uncooled type infrared sensor having awide dynamic range. Finally, since an infrared sensor according to thepresent invention is highly resistant to fluctuations in themanufacturing process, infrared sensors can be manufactured at a highyield on a stable basis.

What is claimed is:
 1. An infrared sensor comprising: an imaging regioncontaining thermoelectric conversion pixels arranged two-dimensionallyin the form of a matrix of a plurality of row and a plurality of columnson a semiconductor substrate to detect incident infrared rays and atleast a row of insensitive pixels having no sensitivity to infraredrays; a plurality of row selection lines arranged in the columndirection in the imaging region; a plurality of signal lines arranged inthe row direction in said imaging region; a plurality of amplifiertransistors connected respectively to said signal lines with respectivefirst coupling capacitors interposed therebetween; a plurality ofsampling transistors arranged respectively between the drains and thegates of said amplifier transistors; a plurality of first storagecapacitors connected respectively to the drains of said amplifiertransistors with respective second coupling capacitors interposedtherebetween; a plurality of first reset circuits configured to resetrespectively the drain potentials of said amplifier transistors; aplurality of clamp circuits configured to clamp respectively thevoltages of said first storage capacitors; and a plurality of readcircuits configured to read respectively the signal charges held in saidfirst storage capacitors.
 2. An infrared sensor comprising: a pluralityof thermoelectric conversion pixels arranged in the form of a matrix ofa plurality of rows and a plurality of columns and configured tothermoelectrically transform the heat generated as a result of absorbingincident infrared rays and take it out as a change in the resistance; aplurality of selection lines connected respectively to either the rowsor the columns of said thermoelectric conversion pixels; a plurality ofsignal lines connected respectively to the other of the columns and therows of said thermoelectric conversion pixels; a pixel selection circuitconfigured to selectively apply a read voltage to said thermoelectricconversion pixels connected to said selection lines and to cause saidsignal lines to generate respective voltage signals; an output signalamplifying circuit having a first input section and a second inputsection, said first input section being connected to said signal lines,and configured to amplify the voltage signal from said thermoelectricconversion pixels; and a voltage generating circuit connected to thesecond input section of said output signal amplifying circuit andapplying a waveform voltage to cancel or reduce the voltage componentcontained in said voltage signal, which is due to the resistance changecomponent attributable to the self heating produced in saidthermoelectric conversion pixels by said read voltage, in synchronismwith said read voltage.
 3. An infrared sensor according to claim 2,wherein said output signal amplifying circuit comprises a plurality ofoutput amplifying circuits connected respectively to said plurality ofsignal lines.
 4. An infrared sensor according to claim 2, wherein eachof said thermoelectric conversion pixels has a thermoelectric conversionsection and a support structure for supporting the thermoelectricconversion section on a cavity structure formed inside saidsemiconductor substrate and the support structure includes a wiretransmitting a signal from said thermoelectric conversion pixel, saidwire being connected to the corresponding one of said selection linesand the corresponding one of said signal lines.
 5. An infrared sensorcomprising: thermoelectric conversion pixels arranged two-dimensionallyon a semiconductor substrate, each having an infrared absorbing sectionconfigured to absorb incident infrared rays and convert them into heatand a thermoelectric conversion section configured to convert thetemperature change produced by the heat generated in the infraredabsorbing section into an electric signal; a pixel selection circuitconnected to said thermoelectric conversion pixels to select one of saidthermoelectric conversion pixels to be used for reading a signal fromit; a pixel signal read circuit configured to read the signal from thethermoelectric conversion pixel selected by said pixel selectioncircuit; an output circuit configured to output said signal read by saidpixel signal read circuit; said pixel signal read circuit including anamplifying circuit configured to amplify the signal from saidthermoelectric conversion pixel, said amplifying circuit having a MOStransistor and configured to receive the output signal of saidthermoelectric conversion pixel through the gate of said MOS transistoras voltage signal; and a voltage applying circuit configured to apply aramp waveform voltage or a step waveform voltage synchronized with pixelselection of said pixel selection circuit to the source of said MOStransistor to suppress the increase of a voltage between the gate andsource of said MOS transistor.
 6. An infrared sensor according to claim5, wherein said voltage applying circuit comprises a voltage generatorgenerating a ramp waveform voltage or a step waveform voltagesynchronized with the pixel selection pulse from said pixel selectioncircuit, said voltage generator being formed on said semiconductorsubstrate.
 7. An infrared sensor according to claim 5, wherein saidvoltage applying circuit comprises a voltage generator generating a rampwaveform voltage or a step waveform voltage synchronized with the pixelselection pulse from said pixel selection circuit, said voltagegenerator being provided outside said semiconductor substrate.
 8. Aninfrared sensor according to claim 5, wherein said pixel selectioncircuit has a pixel selection pulse output terminal and a voltagegenerator generating a rectangular voltage in synchronism with the pulseoutput, said voltage generator being provided outside the semiconductorsubstrate; the rectangular voltage output from the voltage generatorbeing input to said source; an integration circuit having at least anelectric capacitor being added to the current path between the outputterminal of said voltage generator and said source.
 9. An infraredsensor according to claim 8, wherein said pixel selection circuit has aplurality of voltage generators are provided.
 10. An infrared sensorcomprising: thermoelectric conversion pixels arranged two-dimensionallyin a plurality of rows and a plurality of columns on a semiconductorsubstrate, each having an infrared absorbing section configured toabsorb incident infrared rays and to convert them into heat, athermoelectric conversion section configured to convert the temperaturechange produced by the heat generated in the infrared absorbing sectioninto an electric signal and a support structure for supporting saidinfrared absorbing section and said thermoelectric conversion section ona cavity structure formed inside said semiconductor substrate, saidsupport structure containing at least a wire transmitting a signal fromsaid thermoelectric conversion section, said wire being connected to acorresponding row selection line and a corresponding column signal line;a pixel selection circuit configured to apply a pixel selection pulse toeach of said row selection lines to select at least one of saidthermoelectric conversion pixels; a pixel signal read circuit configuredto read the signal from said thermoelectric conversion pixel selected bythe pixel selection circuit through said corresponding column signalline; and an output circuit configured to output said signal read bysaid pixel signal read circuit; said pixel signal read circuit includinga MOS transistor amplifying the signal from said thermoelectricconversion pixel; said amplifying circuit including a circuit forconducting current modulation by applying at least the signal from saidthermoelectric conversion pixel to the gate of said MOS transistor asvoltage signal; each row including at least a thermally isolatedinsensitive pixel having no photo sensitivity to infrared rays andsupported on said cavity structure by said support structure on saidsemiconductor substrate, said thermally isolated insensitive pixelsbeing arranged in the form of an insensitive pixel column, a voltagereferring to a voltage generated in the column signal line of saidinsensitive pixel column being inputted to the source of said MOStransistor.
 11. An infrared sensor according to claim 10, furthercomprising: at least a one step source follower circuit configured toreceive a reference voltage generated from one of said thermallyisolated insensitive pixels to the input thereof, the output of saidsource follower circuit being input to the source of said MOStransistor.
 12. An infrared sensor according to claim 10, wherein eachof said thermally isolated insensitive pixels comprises an infraredreflection layer formed on the surface of the infrared absorbing sectionof a thermoelectric conversion pixel.